disconnect battery, then,
check these connectors for corrosion or water staining on the pins.
This is assuming there is no rodent damage or previous wiring repairs made.
ECM, check ECM and harness connector sides for damaged, discolored or corrosion on pins.
engine to body harness square multi pin connector near fuse main panel.
dizzy and ign module on fender.
check spout connector.
check bulkhead connectors at firewall (the other 2 near ECM).
if all else fails pull ecm out remove cover plates check for water damage, discolored or burned areas on board.
Note, to remove ECM loosen drivers iner fender liner, ecm pulls out towards engine bay. not from under the dash.
next up, if not related to the wiggle test.
does truck have fuel press when no start?
when it dies does it stumble to death, or just shut off?
ign switch, pickup in dizzy.
truck all stock or ????? anything else we should know about history?